code: def testCombiningStat(self):
      for shape in [(), (3,), (3, 4)]:
          li = []
          rs1 = RunningStat(shape)
          rs2 = RunningStat(shape)
          rs = RunningStat(shape)
          for _ in range(5):
              val = np.random.randn(*shape)
              rs1.push(val)
              rs.push(val)
              li.append(val)
          for _ in range(9):
              rs2.push(val)
              rs.push(val)
              li.append(val)
          rs1.update(rs2)
          assert np.allclose(rs.mean, rs1.mean)
          assert np.allclose(rs.std, rs1.std)
  
file_path: ray/rllib/tests/test_filters.py
imports: import numpy
  import unittest
  import ray
  from ray.rllib.utils.filter import RunningStat, MeanStdFilter
  from ray.rllib.utils import FilterManager
  from ray.rllib.tests.mock_worker import _MockWorkerSet
label_desc: Use image node_id 2 for calling the RunningStatTest obj's underlying member method code with example usage: obj.testCombiningStat() without return types